The present invention relates to an optical modulation device such as a display device or an optical valve, and more particularly to a novel liquid crystal optical device adapted to operation of a large number of picture elements in a time-sharing member.
The following structures have been adopted to provide liquid crystal display devices in which a large number of picture elements are arranged in the form of a matrix, but they have their own defects:
(1) Simple electrode matrix: PA1 (2) Structure in which an active element such as a TFT (thin film transistor) is provided for each picture element: PA1 (3) Structure in which an MIM (Metal-Insulator-Metal)structure type nonlinear element is provided for each picture element:
This structure can remarkably simplify the fabrication of liquid crystal display devices, but there arises a problem that an electric field is applied even to non-selected points, resulting in crosstalk. As a result, the number of picture elements cannot be increased.
Each active element can accomplish distinct switching operation so that crosstalk can be prevented, but the fabrication of active elements requires extremely precise alignment technique. As a result, when this structure is applied to the fabrication of liquid crystal devices with a large area, the cost becomes extremely high.
If electrical matching between a nonlinear element and a liquid crystal layer corresponding to each picture element is satisfactory, crosstalk can be prevented and the number of picture elements can be increased. However, when the packing density of picture elements is increased, the electrostatic capacitance of the liquid crystal layer of each picture element is decreased so that the electrostatic capacitance of each nonlinear element must be decreased accordingly in order to obtain electrical matching. The requirement that a nonlinear element must be capable of storing charge as well as severe driving conditions presents an obstacle in respect of fabrication. Methods for driving a liquid crystal with non-linear elements are found and discussed in various papes. For instance, detailed description is contained in "The Optimization of Metal-Insulator-Metal Nonlinear Devives for Use in Multiplexed Liquid Crystal Displays", David R. Baraff et al., Transactions on Electron Devices, Vol. ED-28, No. 6, June 1981. However, even if any of the reported structures is adopted it is difficult to provide a liquid crystal display device with a large number of picture elements, and a large picture screen and relatively inexpensive liquid crystal devices have not been available so far.